<?php
/**
 * PHPExcel
 *
 * Copyright (c) 2006 - 2013 PHPExcel
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 *
 * @category   PHPExcel
 * @package    PHPExcel_Shared_Trend
 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 * @license    http://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt	LGPL
 * @version    1.7.9, 2013-06-02
 */


require_once(PHPEXCEL_ROOT . 'PHPExcel/Shared/trend/bestFitClass.php');


/**
 * PHPExcel_Logarithmic_Best_Fit
 *
 * @category   PHPExcel
 * @package    PHPExcel_Shared_Trend
 * @copyright  Copyright (c) 2006 - 2013 PHPExcel (http://www.codeplex.com/PHPExcel)
 */
class PHPExcel_Logarithmic_Best_Fit extends PHPExcel_Best_Fit {
	/**
	 * Algorithm type to use for best-fit
	 * (Name of this trend class)
	 *
	 * @var    string
	 **/
	protected $_bestFitType = 'logarithmic';


	/**
	 * Return the Y-Value for a specified value of X
	 *
	 * @param     float $xValue X-Value
	 *
	 * @return     float                        Y-Value
	 **/
	public function getValueOfYForX($xValue) {
		return $this->getIntersect() + $this->getSlope() * log($xValue - $this->_Xoffset);
	} //	function getValueOfYForX()


	/**
	 * Return the X-Value for a specified value of Y
	 *
	 * @param     float $yValue Y-Value
	 *
	 * @return     float                        X-Value
	 **/
	public function getValueOfXForY($yValue) {
		return exp(($yValue - $this->getIntersect()) / $this->getSlope());
	} //	function getValueOfXForY()


	/**
	 * Return the Equation of the best-fit line
	 *
	 * @param     int $dp Number of places of decimal precision to display
	 *
	 * @return     string
	 **/
	public function getEquation($dp = 0) {
		$slope = $this->getSlope($dp);
		$intersect = $this->getIntersect($dp);

		return 'Y = ' . $intersect . ' + ' . $slope . ' * log(X)';
	} //	function getEquation()


	/**
	 * Execute the regression and calculate the goodness of fit for a set of X and Y data values
	 *
	 * @param     float[] $yValues The set of Y-values for this regression
	 * @param     float[] $xValues The set of X-values for this regression
	 * @param     boolean $const
	 */
	private function _logarithmic_regression($yValues, $xValues, $const) {
		foreach ($xValues as &$value)
		{
			if ($value < 0.0)
			{
				$value = 0 - log(abs($value));
			}
			elseif ($value > 0.0)
			{
				$value = log($value);
			}
		}
		unset($value);

		$this->_leastSquareFit($yValues, $xValues, $const);
	} //	function _logarithmic_regression()


	/**
	 * Define the regression and calculate the goodness of fit for a set of X and Y data values
	 *
	 * @param    float[] $yValues The set of Y-values for this regression
	 * @param    float[] $xValues The set of X-values for this regression
	 * @param    boolean $const
	 */
	function __construct($yValues, $xValues = array(), $const = true) {
		if (parent::__construct($yValues, $xValues) !== false)
		{
			$this->_logarithmic_regression($yValues, $xValues, $const);
		}
	} //	function __construct()

} //	class logarithmicBestFit
